1. Field of the Invention
The present invention relates to a three-dimensional structure forming apparatus for forming a three-dimensional structure on the basis of an optional stereographic image by irradiating a liquid photosetting resin with a light beam and, more particularly, to a liquid level controller for controlling the liquid level of the liquid photosetting resin contained in a main resin tank.
2. Description of the Prior Art
A method of forming a structure having a desired morphology by irradiating a liquid photosetting resin with a light beam is proposed, for example, in Japanese Patent Application No. Sho 63-267945. FIG. 5 shows an essential portion of a three-dimensional structure forming apparatus 51 for carrying out the method.
The three-dimensional structure forming apparatus 51 has a main resin tank 52 for containing a liquid photo-setting resin A which sets when exposed to ultraviolet rays, a horizontal stage 53 having the shape of a plate and placed in the main resin tank 52, an elevating mechanism 54 for vertically moving the stage 53, a scanning unit 55 for irradiating the surface of the liquid photosetting resin A with a light beam, and a molding controller 56 for controlling the exposure and scanning operation of the scanning unit 55 and the operation of the elevating mechanism 54 for moving the stage 53.
In forming a three-dimensional structure of a desired morphology by the three-dimensional structure forming apparatus 51, the elevating mechanism 54 locates the stage 53 an initial position indicated by continuous lines where the liquid photosetting resin A spreads in a predetermined thickness over the stage 53, and then the surface of the liquid photosetting resin A is scanned with a light beam B for raster scanning in a pattern corresponding to the pattern of one of a plurality of parallel planes obtained by slicing an optical stereographic image, which will be referred to as "parallel decomposed planes".
Portions of the liquid photosetting resin A irradiated with the light beam B set in a hard resin layer of a shape corresponding to the pattern of the decomposed plane. Every time one hard resin layer is formed, the elevating mechanism 54 lowers the stage 53 by a predetermined distance corresponding to the pitch of the decomposed planes of the stereographic image to spread the liquid photosetting resin A over the hard resin layer in a thickness corresponding to the pitch of the decomposed planes. Then, the liquid photosetting resin A spreading over the hard resin layer is scanned with the light beam B in a pattern corresponding to the pattern of the next decomposed plane to form a hard resin layer of a shape corresponding to the pattern of the corresponding decomposed plane on the previously formed hard resin layer. These successive hard resin layers join together.
Thus, hard resin layers of shapes respectively corresponding to the patterns of the decomposed planes are formed successively in adjoining layers to form a desired three-dimensional structure.
Thus, a three-dimensional structure can be formed on the basis of an optical image by this method of forming a three-dimensional structure.
In irradiating the surface of the liquid photosetting resin A contained in the main resin tank 52 with the light beam B by the three-dimensional structure forming apparatus to harden portions of the liquid photosetting resin A in a pattern, the diameter of the spot of the light beam B is dependent on the distance between the objective lens of the three-dimensional structure forming apparatus and the surface of the liquid photosetting resin A. Accordingly, if the liquid level of the liquid photosetting resin A contained in the main resin tank 52 is variable, the diameter of the spot of the light beam B is variable and hence it is impossible to form a three-dimensional structure in accurate dimensions.
The liquid level of the liquid photosetting resin A in the main resin tank 52 is liable to vary with the variation of the temperature of the liquid photosetting resin A or with the reduction of the amount of the liquid photosetting resin A contained in the main resin tank 52.
When a very large main resin tank is used or when the light beam is focused in a very small spot to reduce the terminal depth, in particular, the liquid level of the liquid photosetting resin must precisely be controlled. However, no effective liquid level control system for such a purpose has been developed so far.